Certain viruses have evolved to be able to avoid detection by cytotoxic T cells. These viruses remove the MHC class 1 molecules from the surface of the cell that they are infecting. This ensures that the cytotoxic T cells do not bind to the infected cell and kill the cell and the virus within. Which immune cell is specifically designed to recognize these types of viral threats?

• A. CD4 effector cells.
• B. T helper cells.
• C. Regulatory T cells.
• D. Natural killer cells.
• E. CD8 effector cells.

Answer: (D)

Verified step by step guidance

1. Understand the role of MHC class I molecules: MHC class I molecules are present on the surface of all nucleated cells and are responsible for presenting endogenous antigens, including viral peptides, to CD8+ cytotoxic T cells.
2. Recognize the strategy of certain viruses: Some viruses have evolved mechanisms to evade immune detection by removing MHC class I molecules from the surface of infected cells, preventing CD8+ cytotoxic T cells from recognizing and destroying them.
3. Identify the immune cell that can detect cells lacking MHC class I: Natural killer (NK) cells are a type of lymphocyte that can recognize and kill cells that have low or absent MHC class I molecules, a common feature of virally infected or transformed cells.
4. Differentiate NK cells from other immune cells: Unlike CD8+ T cells, NK cells do not require antigen presentation via MHC class I to recognize and kill target cells. They are part of the innate immune system and can respond quickly to infected or abnormal cells.
5. Conclude the specific immune response: Given the ability of NK cells to detect and eliminate cells lacking MHC class I molecules, they are specifically designed to recognize and respond to viral threats that evade detection by cytotoxic T cells.